Vacuum crystallizer and method of crystallizing



Jan. 5, l1937. -H. B.' CALDWELL 2,057,043

i VACUUM CRYSTALLIZER AND METHOD OF CRY-STALLIZING Filed OCT'. 25, 1935w ff-L :5i

ma@ W, w j@ M W l' Patented Jan. 5, I

UNITED STATES :anni:

PATENT oFFic/B VACUUM CBYSTAILIZEB AND METHODOF "CBYSTALLIZIN umm n.oneven. 'New' rm. N. r., mami :o

Swenson Evapin'atoi' Company, Harvey corporation of Illinois Ill.,a

appnc'emn october g5, 193s, anni No. 695.095

' nomini. l(criss- 45) This invention relates to vacuum crystallizers bya suitable cooling fluid, which may be at a temperature substantiallyhigher than the temperature of the solution from which the crystals arebeing deposited. v ,l lo One ot the principal objects oi the inventionis to provide. an improved method of andapparatus for crystallization. Afurther object of the invention isto provide an improved method of andapparatus for crystalgo lization, which ,is substantially continuous andcan be continued for prolonged periods o! time without ceasingoperations. Other obiectsradvantages and capabilities of the inventionwill appear from the following dem scriptlon oi a preferred embodiment'thereof, I te. .n in commotion with .the accompanying u.: in whicha i '1e 1 is a diagrammatic view ot a crystallizer embodying my invention, and

' a0 Pig. 2 is a sectional view taken on the line 2--2 when the shell isevacuated to a substantial degree,

for example. about 29 inches of mercury, the surface oi' the liquid inthe shell I Il isat a relativelyl low point on the'cylindrical portionthereof, so that ample vapor space is provided above the .surl'aceiorthe ebullition which takes place. Suitable stirring means are providedfor agitatlng the ,liquid wlthinthe shell l0. These'mcans 60 may?`suitably consist o! propellersv M mounted on shaits i! which -are drivenby suitable means (not shown) 'so as to agltate the liquid thoroughly.The solution from which salts are to be crystallined is suppliedby avalved pipe Il. i, The mercado! the shell II isprovldedwlth an openingIl which communicates with a suitable device Il for creating a vacuumwithin the shell lil and compressing the vapors removed from the shell.This evacuating means may be any oi the pumps or electors known in' thisart. 5 In the speciiic embodiment illustrated the ,evacug ating means l1is a booster elector which is supi plied with high pressure steamthrough a pipe i8. y 'I'his steamis supplied to a steam chest I9 fromwhich it passes through a chamber 20 through 10 nozzles 2|. The chamber20 communicates with the opening ii. The nozzles 2| terminate in theconverging portion ot a' venturi 22, which venturi delivers into acondenser 23.` Thecondenser 23 is shown by way of example as comprisinga 15 `chamber through which passes a Icoil 24, through which suiti'iblecooling fluid is' passed. Said chamber communicates with the barometricleg 25 sealed by a trough 2G. The chamber is also Aconnected to a vacuumpump 2l which exhausts air introduced into the system with the liquidsupplied or introduced byleakage.

With an eilicient evacuating means -Il of the type shown and'an'e'ilicient condenser 2,3 'the apparatus thus far described is a veryeiective 25 means for cooling liquid introduced into the shell Il l. Forexample, it is quite feasible to freeze water in the shell i0,notwithstanding thel fact that the cooling water available for use inthecoil 23 is at ordinary summer temperatures. 3@

-lin crystallizing salts from solutions containing them the solution isintroduced by the pipe I5 and the booster ejector il is put intooperation, likewise the vacuum pp 21. 'As a result of the high vacuumproduced in the shell I0, for ex- 35 ample a vacuum of 29 inches ofmercury when the atmospheric pressure stands at 30 inches, a certainamount of ebullition occurs within the shell l0 and the resultingevaporation cools the liquid to a point where crystals deposit to ade-4@ sired extent.-

'Ihe vapors from the'ahell I0 together with the ,steam introduced bypipeI8 are commingled in.

the venturi 22 and are ilnally condensed in the condenser 23. Inpracticing crystallization in 45 this manner I have found that` aconsiderable amount oi salt is deposited on the walls of the shell Ilabove the liquid level, this deposit resulting from the splashing of thechilled solution upon these walls.-V Here the iilm oi liquid is suboo Ilected to the full effect of the vacuum and the water evaporatestherefrom rapidly so that the deposit grows as the crystallization iscontinued. I have also found that the overhead carries with it a certainamount oientrainment which builds 66 up on the nozzles 2|, which nomlesare at high temperature owing to the passage of steam therethrough. Theentrainment hitting these nonies is immediately deprived of its watercontent so that the salts build up thereon.

In order to render the operation continuous I provide within the shellI0, preferably at a position as high as possible therein, a spray Pipe2s which is preferably annular in form and provided with spray openingsadapted to distribute liquid around the whole surface of the cylindricalwall of the shell. This liquid is adapted to iiow downwardly over thissurface and remove any salts deposited thereon or prevent the depositionof any salts thereon. 'I'he pipe 2. communicates with .one or morevalved pipes 2l so that a controlling supply of liquid can be suppliedto pipe 28 continuously or at intervals. The nature of the liquidsupplied to the pipe 2l will depend upon the nature of the precipitateon the walls. or the salt or substance which isbeing crystallized. Thesolvent in the solution being evaporated is always suitable. In manycases where the solution being evaporated is relatively dilute,

a certain portion of the feed supplied to the shell lil may beintroduced by the pipe 2l. In order to remove the, deposit of salts orthe like upon the nozzles 2| I provide a valved pipe 3l adapted todeliver water or other suitable liquid upon these homes. In theembodiment of the invention illustrated I have shown the pipe 3ldelivering into the top wall of the chamber 2l.

' In addition to the supply of liquid by means of the pipe 30, I preferto provide in opposite walls of the chamber 2li, openings 3l for thesupply of further quantities of liquid. .'llheL openings ll arepreferably located near the level of the lowest nozzles 2| so that the.overhead can'ies the spray with it over the outer surfaces of thenoazles whereby the deposit of solute is effectively prevented orremoved. supplied with said liquid by means oi valved pipes 32. It is tobe understood that it is not intended to limit the invention to thisdisposition of the means for supplying liquid to the ejector, since suchmeans may be located in any position whereby they are effectivelyadapted to remove or prevent deposit of the solute on the nonies 2i.While the liquid supplied to the ejector may suitably be a solvent forthe solute, this is not necessary since the removal of the deposit is atleast partially mechanical due to great changes of temperaturefracturing the deposit. I nnd that after running for one hour, that byturning on the liquid supply for three minutes and then turning on thesteam the deposit is substantially fractured and falls from the noles.

In the preferred manner of operating, I prefer to supply a small amount'of liquid continuously by the pipes 2l, that is, an amount of liquidwhich will keep any entrainment striking the walls from depositingcrystals thereon or which will cause crystals on the walls to.remainslushy and become washed down by the stream of liquid.

As stated above, it is preferred to supply liquid by pipes 3l and I2 forshort periods at comparativeLv long intervals, for example, periods oi'about three minutes at intervals of about one hour. l

Although the invention has been described in connection with thespecific details of a prei'erred embodiment thereof, it is not intendedthat such details should be considered limitative of the inventionexcept so far as set forth in the accompanying claims.

The openings 3i are' ,ooaoss Having thus described my invention Ideclare that what I claim is: v

l, A vacuum crystallizer comprising a chamber.

adapted to contain solution and provide a vapor space thereabove, meansfor withdrawing vapors to create a vacuum in the chamber and compressthe withdrawn vapors, cooling means for condensing said compressedvapors, and means for injecting liquid upon surfaces within the vaporspace oi' said chamber in order to prevent accumulation of solutethereon.

2. A vacuum crystallizer comprising a chamber adapted to containsolution and provide a vapor space thereabove, means for withdrawingvapors to create a vacuum in the chamber and compress the withdrawnvapors, cooling means for condensing said compressed vapors, and meansfor injecting liquid upon the internal surfaces of the vapor withdrawingmeans in order to prevent accumulation of solute thereon. Y 3. A. vacuumcrystallizer comprising a shell adapted to contain solution and providea vapor space thereabove, means for withdrawing vapors tocreate a vacuumin the chamber, and means for injecting liquid upon the internalsurfaces of the vapor withdrawing means in order to prevent accumulationof solute thereon.

4. 'Ihe method of crystallizing solute Lfrom solutions which consists insupplying said solution to a closed chamber, maintaining a vapor spaceabove said solution in said chamber, withdrawing vapors from said spaceand maintaining a substantial vacuum therein thereby causing a fall oftemperature below that necessary for the precipitation oi' crystals,injecting -liquid upon surfaces within said vapor space to preventaccumulation of solute thereon andwithdrawing said crystals from saidchamber.

5. 'Ihe method of crystallizing solute from solutions which consists insupplyin said solution to a closed chamber provided with an ejectorcommunicating with the .upper portion of said chamber, withdrawingvaporsfrom said space by said ejector and maintaining a substantialvacuum therein thereby causing a fall of temperature below thatnecessary for the precipitation of crystals, injecting liquid into saidejector to prevent accumulation of solute therein. and withdrawing saidcrystals' from said chamber.

8. A vacuum crystalliser comprising a chamber adapted to containsolution and provide a vapor space thereabove, means for withdrawingvapors to create avacuum in the chamber and compress the withdrawnvapors, said means including ejector tubes adapted to convey steam athigh temperature, cooling means for condensing said compressed vaporsand steam, and means for injecting liquid upon the outer surfaces ofsaid ejector tubes for the purpose oi' removing accumulated solutetherefrom.

7. A vacuum crystallizer comprising a shell adapted to contain solutionand provide a vapor space thereabove, means for withdrawing vapors tocreate a vacuum in the chamber, said means comprising ejector tubesadapted to convey steam at hightemperature, and means for injectingliquid upon the exterior vsurfaces of said ejector tubes, for thepurpose of removing accumulated solute therefrom.

8. The continuous method of crystallizing solute from solutions whichconsists in supplying said solution continuously to a closed chamber soas to pass over unsubmersed portions of the wall thereof so as toprevent deposition of solute thereon, maintaining a Por space above saidsolution in said chamber, continuously withdrawing vapors from saidspace and maintaining a substantial vacuum therein, thereby causing afall of temperature below that necessary for the precipitation ofcrystals, and continuously withdrawing said crystals from said chamber.

9. The continuous method of crystallizing so-y lute from solutions whichconsists in supplying 'said solution to a closed chamber, maintaining avapor space above said solution in said chamber, continuouslywithdrawing vapors from said space and maintaining a substantial vacuumtherein, thereby causing a fall of temperature below that necessary forthe 'precipitation of crystals, continuously injecting liquid uponsurfaces within said vapor space to prevent accumulation of solutethereon, and continuously withdrawing said crystals from said chamber.

10. The continuous method of crystallizing solute from solutions whichconsists in continuously supplying said solution to a closed chamberprovided With an ejector communicating with the upper portion of saidchamber, said ejector comvprising an ejector tube conveying steam athigh temperature, continuously withdrawing vapors from said space bysaid ejector and maintaining a substantial vacuum therein, therebycausing a fall of temperature below that necessary for the precipitationof crystals, intermittently injecting liquid upon said ejector tubes toremove solute deposited thereon, and continuously withdrawing saidcrystals from said chamber.

11. A continuous method of crystallizing solute fromsolutions whichconsists in continuously supplying said solution to a closed chamberprovided with an ejector communicating with the upper portion of saidchamber, said ejector comprising an ejector tube adapted to convey steamat high temperature, continuously withdrawing vapors from said space bysaid ejector and maintaining a substantial vacuum therein, therebycausing a fall of temperature below that necessary for the precipitationof crystals, injecting liquid into said chamber so as to cause theinjected liquid to flow down the unsubmerged walls thereof and preventaccumulation. of solute thereon, intermittently injecting liquid uponthe exterior of the ejector tubes for the purpose of removing solutedeposited thereon, and continuously removing said crystals from saidchamber.

HAROLD B. CALDWELL.

